Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS63 KLOT 022024
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
224 PM CST MON MAR 2 2015

.UPDATE...

HAVE ECHOED THE PREVIOUS SHIFTS CONCERNS FOR MIXED PRECIPITATION
DURING THE TUESDAY MORNING COMMUTE...AND HAVE ISSUED A WINTER
WEATHER ADVISORY FOR THE ENTIRE AREA LATE TONIGHT THROUGH TUESDAY
MORNING. MODELS ARE STILL SHOWING PRECIPITATION BEGINNING AS SNOW
NORTH OF INTERSTATE 80...AND SOME FORM OF SNOW...SLEET OR POSSIBLY
EVEN FREEZING RAIN IN THE FAR SOUTH. IT COULD BE A PRETTY GOOD
BURST OF WET SNOW INITIALLY BEFORE THE TRANSITION BEGINS.

A WARM FRONT WILL LIFT THROUGH THE AREA DURING THE MORNING HOURS.
THIS IS THE PERIOD WHERE MODELS A SHOWING A MORE SIGNIFICANT PUSH
OF PRECIPITATION. WE ARE COMING OUT OF A PRETTY COLD AIR
MASS..AND DEWPOINTS ARE STILL VERY LOW ACROSS THE AREA...WITH
DEWPOINTS ABOVE FREEZING NOT VERY CLOSE. TEMPERATURES LOOK TO
REMAIN BELOW FREEZING THROUGH AT LEAST MID MORNING AREA WIDE.
MODEST PRECIPITABLE WATER VALUES IN EXCESS OF 0.75 INCHES COUPLED
WITH A 35-40 KT LOW LEVEL JET FEEDING INTO THE LOW LEVEL FRONTAL
ZONE WOULD SUGGEST MODEST PRECIPITATION RATES DURING THIS TIME WHEN
THE LOW LEVEL (925-850 MB) TEMPERATURES ARE HEADING ABOVE
FREEZING. SOME OF THE RECENT NAM/GFS WAS SLIGHTLY COOLER IN THE
THERMAL PROFILE FOR THIS PERIOD SUGGESTING THAT SLEET MAY
DOMINATE AND IF PRECIPITATION RATES CONTINUE A BIT HEAVIER THIS
MAY SLOW THE LOW LEVEL WARMING...BUT THE SIGNAL IS STILL THERE
FOR FREEZING RAIN ACCUMULATION. SNOW AMOUNTS MAY BE HIGHER NEAR
THE WISCONSIN BORDER WHERE THE LOW LEVEL WARMING MAY BE A TOUCH
SLOWER.

MORE DETAILS TO FOLLOW THIS AFTERNOON.

KMD

&&

.SHORT TERM...
250 AM CST

THROUGH TUESDAY...

HIGH PRESSURE CENTERED OVER THE MID MISSOURI VALLEY THIS MORNING
WILL TRANSLATE EAST ACROSS NORTHERN ILLINOIS THIS AFTERNOON AND THEN
OFF THE ATLANTIC COAST BY EARLY TUESDAY. MEANWHILE...CLOSED UPPER
LOW WITHIN A DEEP TROUGH IS IN PLACE ACROSS THE WEST COAST AND LEAD
WAVE IS PROGGED TO EJECT NORTHEAST FROM THE DESERT SOUTHWEST THIS
EVENING WITH A SURFACE LOW DEVELOPING OVER THE COLORADO FRONT RANGE
WHICH WILL LIFT INTO THE UPPER MIDWEST TUESDAY. THIS WILL BE A
CHALLENGING SYSTEM WITH THE POTENTIAL FOR MODEST SNOW ACCUMULATIONS
ON THE FRONT END...IN ADDITION TO LIGHT ICE ACCUMULATIONS...BEFORE
PRECIPITATION CHANGES OVER TO ALL RAIN. THESE DETAILS OF COURSE WILL
HINGE ON THE TRACK AND STRENGTH OF THE LOW WHICH MODELS CONTINUE TO
STRUGGLE WITH. THE 00Z EUROPEAN MODEL FITS WELL WITHING THE BEST
CLUSTERING OF THE GEFS AND HAS SHIFTED NORTH FROM PREVIOUS RUNS...A
MOVE THE GFS MADE WITH EARLIER GUIDANCE...THOUGH THE LATEST RUN IS
NORTH OF THE GEFS MEAN. SREF IS EVEN AN FARTHER NORTHERN OUTLIER.
CONTINUE TO LEAN HEAVILY ON THE ECMWF GUIDANCE BUT WITH A NORTHERN
STREAM SYSTEM PUSHING EAST ACROSS THE CANADIAN PRAIRIES AND HIGH
PRESSURE ALONG THE EAST COAST...WOULDNT BE SURPRISE TO SEE FARTHER
SHIFTS NORTH WHICH WOULD LIKELY LESSEN THE IMPACTS FROM FROZEN
PRECIP TYPE.

CURRENT EXPECTATIONS ARE THAT PRECIPITATION WILL BEGIN AS SNOW WITH
LIGHT ACCUMULATIONS POSSIBLE BEFORE MID LEVELS WARM ENOUGH FOR A
TRANSITION TO SLEET AND FREEZING RAIN DURING THE MORNING. AS
SURFACE/BOUNDARY LAYER TEMPS CONTINUE TO WARM...PRECIP SHOULD CHANGE
OVER TO RAIN FOR MOST IF NOT ALL OF THE CWA BY AFTERNOON. GIVEN THE
RAPID WARMUP...ANY SNOW/ICE ACCUMULATIONS WOULD LIKELY QUICKLY MELT
OFF. UNFORTUNATELY THE BEST CHANCES FOR FROZEN PRECIP WILL BE RIGHT
AROUND THE MORNING COMMUTE. MID LEVEL DRY SLOT PUNCHES INTO THE
REGION MID AFTERNOON INTO THE EARLY EVENING AND PRECIPITATION WILL
LIKELY TRANSITION TO A LIGHT RAIN OR DRIZZLE...THEN MOST OF THE
REMAINING PRECIPITATION SHOULD START TO PUSH EAST OF THE FORECAST
AREA THROUGH THE EVENING.

DEUBELBEISS

&&

.LONG TERM...
250 AM CST

TUESDAY NIGHT THROUGH SUNDAY...

HIGH PRESSURE WILL GRADUALLY BUILD FROM THE NORTHERN PLAINS TUESDAY
NIGHT TO THE MIDWEST THURSDAY THEN TO THE MID-ATLANTIC COAST FRIDAY
INTO SATURDAY. RIDGING WILL BE IN PLACE ACROSS NORTHERN ILLINOIS
MUCH OF THE PERIOD BRINGING AN EXTENDED PERIOD OF DRIER WEATHER. THE
HIGH WILL BE ACCOMPANIED BY COLDER AIR...WITH H85 TEMPS PUSHING -20C
MOVING ACROSS NORTHERN ILLINOIS WEDNESDAY NIGHT AND THURSDAY
MORNING. THIS WILL BE THE COLDEST MORNING IN THE FORECAST WITH NEAR
OR BELOW ZERO LOWS EXPECTED. A LOW PRESSURE SYSTEM WILL MOVE ACROSS
NORTHERN ONTARIO FRIDAY WITH A THERMAL RIDGE OVERSPREADING NORTHERN
ILLINOIS RESULTING IN WARMER CONDITIONS BY THE END OF THE WEEK INTO
THE WEEKEND.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* LIGHT/VARIABLE WINDS THIS AFTERNOON BEFORE FLOPPING SOUTHEAST BY
  EARLY EVENING. SOUTH-SOUTHEAST WINDS BECOMING GUSTY 20-25 KT BY
  TUESDAY MORNING.

* SNOW...MIXING WITH SLEET THEN CHANGING TO FREEZING RAIN/RAIN
  EARLY TUESDAY MORNING. VFR CONDITIONS TO QUICKLY DETERIORATE TO
  IFR/LIFR IN PRECIP.

KJB

//DISCUSSION...UPDATED 18Z...

IT WILL CONTINUE TO BE A QUIET WEATHER DAY ACROSS THE AREA TODAY. A
SURFACE RIDGE OF HIGH PRESSURE PUSHING ACROSS THE AREA THIS
AFTERNOON WILL RESULT IN A PERIOD OF LIGHT AND VARIABLE
WINDS...THOUGH THE WINDS SHOULD SETTLE INTO A SOUTHEASTERLY DIRECTION
BY EARLY THIS EVENING. OTHERWISE VFR CONDITIONS EXPECTED.

THE WEATHER WILL BECOME MUCH MORE PROBLEMATIC BY DAYBREAK TUESDAY.
WINDS WILL INCREASE OUT OF THE SOUTHEAST AND BECOME GUSTY DURING THE
MORNING. SNOW WILL ALSO DEVELOP OVER THE AREA JUST PRIOR TO
DAYBREAK...BEFORE MIXING WITH SLEET AND CHANGING OVER TO A PERIOD OF
FREEZING RAIN BY MID MORNING TUESDAY. IT CURRENTLY APPEARS THAT
ABOUT A 1 TO 3 HOUR PERIOD OF SNOW AND SLEET WILL OCCUR FROM ROUGHLY
11 UTC THROUGH 13 TO 15 UTC. DURING THIS PERIOD IFR VIS IN SNOW AND
LOWERING CIGS ARE LIKELY. CIGS WILL CONTINUE TO DETERIORATE INTO THE
IFR AND LIFR CATEGORIES DURING THE MORNING AS WARMER AIR ALOFT
BEGINS TO CHANGE THE SNOW AND SLEET OVER TO SOME FREEZING RAIN.
SURFACE TEMPERATURES SHOULD ALSO BE ON A WARMING TREND DURING THE
MORNING...AND ARE EXPECTED TO WARM ABOVE FREEZING BY MIDDAY...SO ANY
LINGERING PRECIP AFTER THIS TIME WILL LIKELY NO LONGER PRODUCE A
FREEZING THREAT.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* MEDIUM-HIGH IN PRECIP TIMING/TREND EARLY TUESDAY. MEDIUM IN
  CIG/VIS IMPACTS.

* HIGH ALL OTHER ELEMENTS.

KJB

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...MVFR CIGS. GUSTY WEST WINDS.

WEDNESDAY...MVFR CIGS.

THURSDAY AND FRIDAY...VFR.

SATURDAY AND SUNDAY...MVFR CIGS POSSIBLE.

RATZER

&&

.MARINE...

224 PM...HIGH PRESSURE OVER THE SOUTHERN LAKES AND OHIO VALLEY
WILL MOVE EAST TO THE MID ATLANTIC AND NEW ENGLAND TUESDAY MORNING
AS LOW PRESSURE FORMS OVER THE CENTRAL PLAINS TONIGHT. THIS LOW
WILL QUICKLY MOVE NORTHEAST TUESDAY AND BE ABSORBED BY STRONGER
LOW PRESSURE OVER NORTHERN ONTARIO...AS A COLD FRONT MOVES ACROSS
LAKE MICHIGAN. THE GRADIENT WILL SLOWLY INCREASE AHEAD OF THIS LOW
TONIGHT INTO TUESDAY MORNING WITH 30 KTS EXPECTED BY TUESDAY
MORNING AND THERE COULD BE SOME LOW END GALE GUSTS BUT CONFIDENCE
REGARDING FREQUENCY IS LOW. WINDS WILL SHIFT TO THE SOUTHWEST IN
THE AFTERNOON AND THEN TO THE NORTHWEST TUESDAY NIGHT. SPEEDS WILL
LIKELY REMAIN IN THE 30 KT RANGE...ESPECIALLY ACROSS THE SOUTHERN
TWO THIRDS...AS HIGH PRESSURE BUILDS ACROSS THE PLAINS WEDNESDAY
AND COLD AIR OVERSPREADS THE REGION. THIS HIGH WILL EXTEND FROM
THE SOUTHERN PLAINS TO THE OHIO VALLEY THURSDAY AS WINDS TURN MORE
WESTERLY AND BEGIN TO SLOWLY DIMINISH. BUT AS THE HIGH DEPARTS
THURSDAY NIGHT...THE GRADIENT WILL TIGHTEN AS LOW PRESSURE MOVES
ACROSS NORTHERN ONTARIO WITH A PERIOD OF SOUTHWEST WINDS TO 30 KTS
ON FRIDAY...WITH SOME LOW END GALES POSSIBLE. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER WEATHER ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-
     ILZ010-ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-
     ILZ022-ILZ023-ILZ032-ILZ033-ILZ039...3 AM TUESDAY TO NOON
     TUESDAY.

IN...WINTER WEATHER ADVISORY...INZ001-INZ002-INZ010-INZ011-INZ019...3
     AM TUESDAY TO NOON TUESDAY.

LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...6 AM TUESDAY TO 6 PM WEDNESDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.